Research in the BMJ looking at long-term data for 100,000 people in five European countries found evidence of harm, even at permitted concentrations.

Experts stressed that the risk to an individual was still relatively small.

And some argued the results were not conclusive as they did not take account of previous exposure to higher levels.

One can only hope that our European politicians will be persuaded of the importance of these findings and reassess their position on air pollution in EuropeProf Jon Ayres , University of Birmingham

Other factors, such as smoking or having high blood pressure, contribute more to a person's risk of heart attack than pollution from traffic fumes and industry, they say.

But repeated, long-term exposure to air pollution - living next to a busy road in a city, for example - does take its toll, the research, involving a collaboration of European universities and institutes, reveals.

Tougher limits

The BMJ study found that for each 5 µg/m3 increase in annual exposure to fine-particulate (PM 2.5) air pollution - thought to be the most damaging type, as smaller particles can penetrate deep into the body - there is a 13% relative increase in the incidence of heart attacks, even after taking into account other risk factors such as smoking.

Similarly, rising levels of larger-particulate air pollution (PM 10) were also linked to heart-attack risk.

And these associations remained even when exposure concentrations were below the current European limits.

Authors of the study - the largest ever looking at the impact of pollution exposure in European people - says its results support the case for lowering EU limits for particulate matter air pollution.

Current EU legislation sets the annual mean limit on PM 2.5 at twice that recommended by the World Health Organization.

Case 'not made'

Jon Ayres, professor of environmental and respiratory medicine at the University of Birmingham, said: "There is no doubt that further reduction of PM levels would result in improvements in cardiac health in Europe.

"One can only hope that our European politicians will be persuaded of the importance of these findings and reassess their position on air pollution in Europe."

Prof David Coggon, from the Department of Occupational and Environmental Medicine at the University of Southampton, was more cautious.

"This study adds to the evidence that particulate air pollution is a cause of heart disease, but it does not establish that there are important health risks from levels of exposure below current exposure limits," he said.

"This is because the differences in risk that were observed may have been a long-term effect of exposures in the past when levels of pollution were higher."

UK estimates suggest nearly 30,000 people die prematurely each year as a direct result of exposure to air pollution, which has been linked to asthma and other lung diseases, including cancer, as well as heart problems.

A recent report by Defra on the issue says evidence suggests that there is no "safe" limit for exposure to PM 2.5, and that this type of man-made pollution cuts the average life expectancy of people living in the UK by seven to eight months.

A Defra spokeswoman said: "Air quality has improved significantly in recent decades and the UK currently meets the EU limits for this type of pollution.

"We want to keep improving air quality and reduce the impact it can have on human health and the environment."